I am wanting to make a cake similiar to the yellow one on the left but I don't know if the yellow dots are buttercream Does anyone have any idea what they could be made of? I really want my dots to look clean like those but didn't think buttercream would give me such perfect spots.

You can pipe them from white chocolate, let it set, then add them to the cake one by one or a very perfect look

Oooh! that is a great idea thank you!

You can also pipe them in advance in buttercream, let them air dry, then place them on your iced cake. That's what I had done for this one:
http://cakecentral.com/gallery/1377678/polka-dot-wedding-cake

I'd pipe them directly on the cake and smash the peaks down a minute or two later.